1. Field of the Invention
The present invention relates to a drive control apparatus for controlling the position and/or velocity of an apparatus being driven, such as a motor, in accordance with a feedback signal provided by position detecting means attached to the driven apparatus.
2. Description of the Related Art
FIG. 6 is a block diagram of a conventional drive control apparatus 11. In this arrangement, position detector 1 detects the position or velocity of a motor 2. A two-phase pulse generator 3 in the position detector 1 generates two-phase pulses according to the angular value of the motor 2. Counters 4 and 5, disposed in drive control apparatus 11 and position controller 5, count the number of pulses output by the two-phase pulse generator 3.
Position controller 5 further comprises a position command generator 26 which provides a position command signal to position control unit 7. Position control unit 7 outputs a velocity command signal to drive control apparatus 11 in accordance with the position command signal, provided by the position command generator 26, and the output signal provided by counter 6, which represents the number of pulses provided by the two-phase pulse generator 3 indicating the current position of the motor 2. Arithmetic unit 8 (CPU 8) then provides a control signal to inverter 9 in accordance with a signal provided by counter 4, representing the number of pulses provided by the two-phase pulse generator 3, and the velocity command signal provided by the position control unit 7.
The operation of the conventional apparatus will now be described in accordance with FIGS. 6 through 8. FIGS. 7 and 8 illustrate the output signals of the two-phase pulse generator 3, designated "A" and "B" in FIG. 6, during forward and backward rotation, respectively. As shown in FIG. 7, the pulses of signal A lead those of signal B by a phase angle of 90 degrees, and the number of pulses output is proportional to the angular position of the motor 2. Conversely, in FIG. 8, the pulses of signal A lag signal B by a phase angle of 90 degrees. Accordingly, the polarity of the phase shift between signal A and signal B represents the rotational direction of the motor 2, while the number of pulses of signals A and B represent the rotational position of the motor 2. Further, the frequency of the pulses represents the speed of the motor 2.
As shown in FIG. 6, signals A and B are input into the counter 4 in drive control apparatus 11, and further into the counter 6 in position controller 5. Counter 6 counts the number of pulses in signals A and B, and the position control unit 7 interprets these values as the angular position of the motor 2. The position control unit 7 provides the velocity command signal to the drive control apparatus 11 according to the position command generated by the position command generator 26 and the current position of the motor 2 as indicated by the signal provided by counter 6. Also, counter 4 in the drive control apparatus 11 counts the number of pulses in signals A and B in a manner similar to counter 6 in the position controller 5. The CPU 8 then reads the value of the counter 4 at a predetermined time "t". When the "n"th value is read, and represented as P(n), the CPU 8 calculates the current velocity V(n) of the motor 2 in accordance with the following formula: EQU V(n)=(P(n)-P(n-1))/t
CPU 8 then outputs a control signal, which controls the drive voltage of the motor 2, to the inverter 9 in accordance with the velocity command signal from the position controller 5 and the current velocity V(n) of the motor 2 as calculated from the signals provided by counter 4. The inverter 9 pulse width modulates (PWM) power provided by a three-phase alternating-current power supply 10 in accordance with the control signal and thereby controls the drive voltage provided to the motor 2.
A second conventional apparatus using a current position display device will now be described in accordance with FIG. 9. The apparatus shown in FIG. 9 comprises a velocity setting device 30, a current position display device 36, a decoder 28 which converts the data of the counter 6 into display data, and a display 29. The other components identical to those described in the first conventional apparatus are identified by the same reference numeral and will not be described.
As in the first conventional apparatus described with reference to FIG. 6, the two-phase pulse signals A and B generated by the two-phase pulse generator 3 in position detector 1 are input into counter 4 in the drive control apparatus 11 and the counter 6 in the current position display device 36. The counter 4 counts the number of pulses in the two-phase pulse signals A and B, and the CPU 8 outputs the control signal to control the drive voltage being provided to the inverter 9 in accordance with the velocity command from the speed setting device 30 and the velocity of the motor 2 as indicated by the signal provided by counter 4. Also, counter 6 counts the number of pulses present in two-phase pulse signals A and B in a manner similar to counter 4 and output a signal representing this count value to the decoder 28. The decoder 28 converts this signal into the display data indicating the position of the motor, and the display device 29 displays this data.
A third conventional apparatus comprising a position detector which outputs position data of an apparatus such as a motor in the form of serial data instead of pulse trains will now be described in accordance with FIG. 10.
The apparatus shown in FIG. 10 comprises a position detector 12 having a position data generating device 13 and a serial data transmission device 14. The apparatus further comprises a drive control apparatus 16 having a serial data receiving device 15, CPU 8 and inverter 9. Other components identical to those described in FIG. 9 are not described with reference to FIG. 10.
As shown in FIG. 10, the position data generating section 13 always generates numerical data representing the position of the motor 2. The serial transmission device 14 converts this data into serial data and transmits this serial data to the serial data receiving device 15. As is well known in the art, in serial transmission, binary data is transmitted in series one bit at a time using a single signal line. The serial data receiving device 15 converts the received serial data into position data that is compatible with the CPU 8. The CPU 8 reads this position data at a predetermined time "t" and calculates the velocity v(n) of the motor according to the following equation: EQU V(n)=(PF(n)-PF(n-1))/t
where PF(n) and PF(n-1) represent the position data being read at time t and a predetermined time interval prior to time t, respectively.
CPU 8 then outputs the control signal, for controlling the drive voltage, to the inverter 9 in accordance with the velocity V(n) of the motor 2, and the velocity command signal provided by the speed setting device 30. The inverter 9 pulse width modulates (PWM) power provided by the three-phase alternating-current power supply 10 in accordance with the control signal to thereby provide the motor 2 with the drive voltage.
As compared to the first or second conventional apparatus as shown in FIG. 6 or FIG. 9, the third conventional apparatus of FIG. 10 has less data transmission lines connected between the position detector 12 and the drive control apparatus 16. Thus, cost can be reduced and a wiring space can be saved.
However, the conventional drive control apparatus of FIG. 10 using serial data is incompatible with the position controller apparatus of FIGS. 6 and 9 which are designed to receive two-phase pulses. Also, in all of the above conventional apparatuses, it is impossible to check or adjust the operation of the drive control apparatus and the position controller if the apparatus being driven (e.g., the motor) and the position detector are not connected to the drive control apparatus.